This invention relates to a generally vertical caster which produces metallic cast products such as bar, strip or slab from molten metal. The invention also includes a method of producing metallic cast product from molten metal and an associated metallic cast product.
Continuous casting of metallic bar, strip and slab is a well known process. One example of such a process is casting aluminum bar using a wheel-type caster. The aluminum bar is used as a starting product for producing aluminum rod and aluminum wire. The advantage of a continuous casting process over the conventional process of producing aluminum rod and wire from extruded, large (fifteen inches in diameter) billets is that the continuous casting process collapses certain manufacturing process steps resulting in the elimination of certain equipment and work stations. This, in turn, significantly reduces capital, labor, maintenance and energy consumption.
The known wheel-type continuous bar caster involves providing a revolving wheel having a trapezoidal groove in which molten aluminum is cast. The groove is covered by a steel or copper belt as the wheel and the cast molten aluminum revolve. The groove and the belt form a mold for casting the aluminum bar. The molten aluminum solidifies in the groove and then exits the wheel of the caster. The solidification process is accomplished by introducing a coolant on the back side of the belt and on the sides of the mold. After solidification, the aluminum bar is introduced into a shape rolling mill where the bar is shaped into aluminum rod. The aluminum rod is then quenched, lubricated and wound onto a coil.
Well known methods and apparatus for continuous casting of metal stripbetween belts are disclosed in U.S. Pat. Nos. 4,061,178 and 4,964,456, among others.
As is well known to those skilled in the art, the quality of the continuously cast aluminum product mainly depends on the thermal conditions during the solidification process. The rate of heat extraction has to be controlled in order to resist (i) surface liquation; (ii) build-up of residual stresses during solidification which can cause side cracking and break-up during casting or subsequent processing; and (iii) centerline segregation of alloying elements. Although many process improvements have been made to the wheel-type caster, the above problems are present, especially in casting certain alloys, such as 2XXX, 5XXX, 6XXX and 7XXX aluminum alloys.
Surface liquations are caused by the formation of an air gap between the solidifying aluminum product and the mold which causes remelting of the shell surface of the cast product. This problem can be solved by maintaining contact between the mold and the solidifying aluminum throughout the length of the casting process. However, as the wheel-type caster has a rigid mold on three sides, it is difficult, if not impossible, to maintain mold/cast product contact throughout the solidification process. In addition, the mold and belt will distort unpredictably thus also making it difficult to maintain mold/cast product contact. Thus, there is a need for a bar casting process and apparatus that provides good mold/bar contact to resist surface liquation and to improve general surface quality of the cast product.
The partially solidified product bending in the round wheel mold causes side bar cracking and product break-up during casting and rolling. Different alloys exhibit different propensities for build-up of residual stresses. This problem is related to heat transfer rates over the length of the solidification zone and can be controlled by careful manipulation of coolant application at strategic locations in the casting process. This requires a casting process with flexibility to vary heat transfer rates over the solidification zone, so that different alloys can be successfully cast. Although improvements in manipulating the coolant application in the wheel-type caster have been made, there is still needed a casting process and apparatus that provides flexibility to vary heat transfer rates over the length of the solidification zone.
In addition, for longer freezing range alloys (i.e., 2XXX, 4XXX, 6XXX and 7XXX) there must be a very efficient coolant application apparatus in order to quickly extract heat from the solidified metal. The wheel-type caster does not provide the type of high cooling rates that are needed to efficiently solidify the cast product. The inefficient cooling causes centerline segregation of the alloying elements which is a universally undesirable result. Thus, there is still needed a caster having a cooling system which efficiently removes heat from the cast molten metal in order to form high quality cast aluminum product.